In order to achieve desirable functionality and operating speed of electronic devices, semiconductor packages used therein are usually incorporated with passive components, such as resistors, capacitors and inductors, for enhancing and stabilizing performances of the electronic devices. The passive components are typically mounted on a surface of a circuit board such as printed circuit board or semiconductor package substrate, wherein the passive components can be located at corners of the substrate or outside a chip attach area on the substrate. However by this arrangement, the passive components not only occupy the surface area of the substrate but also adversely affect the trace routability on the substrate; besides, certain surface area of the substrate is reserved for bond pads, which thus limits the number of passive components capable of being mounted on the substrate, and is not favorable for development of highly integrated packages. Further, in the case of more passive components required for a performance-enhanced package, the substrate needs to be enlarged to accommodate the plurality of passive components and semiconductor chips, such that the package size would be significantly increased and not compliant with the trend of profile miniaturization.
Accordingly, there are developed embedded passive components in a substrate or circuit board which is sought to be thin, multi-layered and of high density by advanced lamination technology. FIG. 1 shows a conventional multi-layer circuit board 10 embedded with a film of capacitive material 11. The capacitive material 11 is a dielectric material having a high dielectric constant, such as polymers, ceramics, polymers with ceramic powders, and the like. In particular, the capacitive material 11 can be barium titanate, lead zirconate titanate or amorphous hydrogenated carbon, dispersed in a binder such as resin, glass powders, and so on. The film of capacitive material 11 can be formed by a sputtering, printing or roller coating process. The film of capacitive material 11 is sandwiched between two patterned circuit layers 12 each comprising several trace regions serving as electrode plates for capacitors, such that a plurality of capacitors can be formed and embedded in the circuit board 10.
The materials and methods for forming passive components such as resistors or capacitors in a laminated circuit board are well focused, and the critical aspect is how to embedded the passive components in the circuit board. Related prior arts include, for example, U.S. Pat. Nos. 3,857,683, 5,243,320, and 5,683,928; most of them are to form the passive components using a printing and/or photoresist-etching process on an organic insulating surface of a patterned circuit layer before forming a new laminated layer on the circuit board during its fabrication. However, when the capacitive material e.g. polymer is applied over the circuit layer, the polymeric material having poor fluidity can hardly effectively fill the spaces between adjacent traces of the circuit layer thereby leaving unfilled gaps, such that the thickness of the capacitive or polymeric material is not easily made even, making a subsequent circuit layer formed thereon not having good planarity. Those drawbacks not only degrade the electrical performance of a fabricated circuit board, but also affect the reliability of a subsequently formed build-up structure for a circuit board.
Therefore, the problem to be solved herein is to provide a capacitor structure embedded in a multi-layer substrate or circuit board, which eliminates the above drawbacks and thereby assures the electrical performance and reliability of the substrate or circuit board.